Fertiliser – Good or Bad?
What Is Fertiliser?
A fertiliser is any natural or synthetic material applied to soil or leaves to supply plant nutrients needed for growth.
Fertilisers can be:
- Organic or synthetic
- Liquid, powder, or granules
- Fast-acting or slow-release
Do I Need Fertiliser?
The Short Answer
No… perhaps and yes.
Why You Don’t Always Need Fertiliser
Look around at:
- Roadside verges
- Motorway embankments
- Trees and shrubs in the countryside
They grow perfectly well without fertiliser. Why?
Because nothing is removed from the system.
Plants use sunlight to turn nutrients in the soil into leaves, flowers, berries, and seeds. When these die and fall, they return to the soil, recycling nutrients naturally. Over time, soil fertility can even increase.
Why You Do Sometimes Need Fertiliser
As gardeners, we remove plants from the cycle:
- Picking flowers
- Harvesting fruit and vegetables
- Removing roots
- cutting grass
Every harvest removes nutrients from the soil.
The more you take out, the more you need to put back in.
Fertiliser simply replaces what has been removed, helping plants continue to grow and crop well.
Why Do We Use Fertilisers?
Plants need sun, water, and nutrients to grow.
If even one essential nutrient is missing, growth is limited.
When nutrients are available:
- Plants grow stronger
- Crops yield more
Large-scale trials by the UN Food and Agriculture Organization showed fertiliser use increased wheat yields by around 60% on average, however this effect can be short lived as the soil gradually deteriorates
Are Fertilisers “Plant Food”?
No.
Think of fertilisers as ingredients, not food.
Plants make their own food through photosynthesis, using sunlight, water, and nutrients.
What Do Plants Actually Need?
The Big Three (Actually Free)
Plants get these naturally from air and water:
- Carbon
- Hydrogen
- Oxygen
The Big Three (Supplied by Soil or Fertiliser)
- Nitrogen (N) – growth and green leaves
- Phosphorus (P) – roots, flowers, energy
- Potassium (K) – strength, health, disease resistance
Secondary Nutrients (Small Amounts)
- Calcium – cell walls and growing points
- Magnesium – essential for chlorophyll
- Sulphur – protein formation
Trace Elements (Tiny Amounts)
Includes:
- Iron
- Boron
- Copper
Healthy soil rich in organic matter usually supplies these naturally.
Organic vs Synthetic Fertilisers
Organic Fertilisers
- Made from natural materials (manure, compost, bone meal, plant matter)
- Nutrients released slowly over time
- Improve soil structure and soil life
- Feed plants and soil microbes
Best used regularly to build long-term soil health.
Synthetic Fertilisers
- Chemically processed
- Water-soluble and fast acting
- Nutrients available immediately
Overuse can burn plants and damage roots.
They do little to improve soil health and can leach into waterways.
Very useful in early spring, when soil microbes are inactive and plants still need nutrients.
The Best Approach
For long-term garden health:
- Build soil with organic fertilisers and compost
- Use synthetic fertilisers carefully when plants need a quick boost
Healthy soil = healthier, more resilient plants.
Different Ways Plants Are Fed
Feeding Through the Soil
- Soil acts as a nutrient reservoir
- Microbes constantly convert nutrients into plant-available forms
In gardens, soil fertility builds over time.
In containers, food runs out quickly and must be replaced regularly.
Feeding Through the Leaves (Foliar Feeding)
Plants can absorb nutrients through their leaves:
- Acts like first aid
- Useful when roots aren’t working efficiently
- Nutrients absorbed 8–20 times faster than through roots
Modern biostimulants work especially well as foliar feeds.
Best times to foliar feed:
- Transplanting
- New growth
- Flowering
- Just after fruit sets
Top Tip
Fertilisers aren’t good or bad—it’s how and why you use them.
If you harvest plants or grow in pots, fertiliser helps replace what’s lost.
Focus on healthy soil first, then feed plants as needed.
